PROJECT SUMMARY ABC transporters are found in all known organisms. Overexpression of ABC multidrug transporters is a major cause of clinical resistance to antibiotics, antifungal and antitumor agents. We use the yeast Pdr5 multidrug efflux pump as a model to study an important subfamily of efflux pumps found only in fungi including the highly pathogenic Candida and Cryptocoocus species. In particular we are interested in learning how these complex, polytopic proteins hydrolyze ATP in the nucleotide-binding domains and then use the resulting chemical energy to transport drugs from the transmembrane domains located a good distance away. We used a combination of suppressor genetics, site-directed mutagenesis, and biochemical assays to begin to identify a transmission signal pathway of amino acid residues and will continue that work as described in this proposal to determine whether the pathway we identify by functional studies is similar to the one proposed by purely structural studies of more conventional transporters. If this is the case, such a result would suggest that this interface is conserved among even evolutionary distant drug transporters. Such an observation might lead to the design of agents that reduce pump activity during treatment.